The experimentally produced take-off of one pigeon is sufficient to induce nearly instantaneous flight in another bird, provided that the take-off is not preceded by preflight activities (e.g., "intention movements") which predict its occurrence. Thus, the "meaning" of the take-off as a social alarm signal depends on the behavioral context in which it occurs. This study seeks to replicate laboratory findings under field conditions and to examine the implication that pigeons in a flock must monitor one another's behavior almost constantly in order for such a signaling system to function effectively. Since ethological reports generally appear to disagree with the present account of the "contagion of flight" phenomenon, some possible exceptions or qualifications to this system will also be investigated. Finally, further efforts will be made to determine if the take-off itself provides any visual or auditory cue for eliciting observers' flight reactions.